The present invention relates to a device for thermally insulating one or more elements of a subsea installation from ambient cold sea water.
In connection with oil and gas producing installations it is well known that cooling of the production fluid and high fluid pressure may result in the formation of hydrates, which may cause clogging of pipes and pipe connections. Cooling of the production fluid may be caused by ambient cold sea water, particularly during a temporary interruption of the production. To delay cooling of the production fluid in case of an interruption of the production, some form of thermal insulation and heat storage medium has to be provided to the element through which the production fluid flows. The element could for instance be a pipe, a manifold, a valve, a connector etc. WO 01/63088 A1 and WO 2006/106406 A1 disclose the use of a so-called heat bank for thermally insulating an element included in a subsea installation. The heat bank comprises a casing, which is arranged to enclose a fluid having heat-storing capacity, for instance water, and which has an internal space for receiving the element and the fluid with the fluid surrounding the element so as to allow the fluid to delay cooling of the element by means of heat stored in the fluid. The casing and the fluid enclosed therein form a thermal barrier between the element and the ambient sea water on the outside of the casing. By means of heat stored in the fluid inside the casing, the heat bank protects the element from cooling too rapidly. The fluid in the heat bank is heated by heat emitted from the protected element during normal operation. This heat emanates from the production fluid flowing through the element. If the heat input to the protected element from the production fluid is decreased or interrupted for some reason, the heat stored in the fluid inside the casing will slow down the cooling of the protected element caused by the ambient cold sea water on the outside of the casing.